This invention relates to a method for disposal of solid waste, particularly chrome residues produced in the production of chromates. Chrome residues constitute one of the major pollution sources, for, besides oxides of magnesium, calcium, silicon, etc., they further contain 2.5-4% of chrome oxidates, wherein the content of water-soluble and acid-soluble chrome ions with a valency of 6 are 0.28-1.34% and 0.91-1.49%, respectively, and these are very harmful to humans and animals.
In recent years, there have been lots of reports concerning methods for toxicity elimination of chrome residues, among which the common method is to reduce six-valency chrome to three-valency chrome, followed by deep burial conservation, such as reduction toxicity elimination of dry- or wet-method. However, a serious problem existing with such methods is that Cr3+ reduced from Cr6+ can be raised back to Cr6+ again, especially when CaO, MgO exists in the chrome residues, since such form conditions for Cr3+ to be raised.
In the meantime, chrome residues can be used as a raw material, thus opening up a new path for treatment of the same. For example, they can be used as a glass coloring agent, for the making of color cement, and for making of bricks, mineral wool, etc. Such use, however, could become a second source of pollution due to dust rising; and then, an industrialized production is impractical since the market demand for such material is too little.
Recent reports from the U.S.A. disclosed a method of inserting electrodes in the chrome residues, to attain a high temperature and melt the residues into a glass material, thus eliminating the toxicity of the same. That method, however, consumes too much energy, and cannot realize a thorough toxicity elimination.
Toxicity elimination methods developed during the past 20 years generally involve the use of hydrochloric acid for melting the chrome residues. A Chinese patent application CN 85 1 05628 disclosed a method, as stated above. Such methods mostly control the pH value of the residues solution between 1 and 2, while a reductant is added to reduce Cr6+ to Cr3+ at a high reaction temperature. Nevertheless, due to large quantities of hydroxide colloids produced in the reaction, it is very difficult to separate the solid and the liquid. Therefore, the problem of preventing Cr3+ from being raised back to Cr6+ remains unsolved.